Abstract

Insitu YBa2Cu3O7−x(YBCO)films have been fabricated on SrTiO3 (001) and LaAlO3 (001) substrates by on‐axis biased‐radio‐frequency magnetron sputtering in Ar‐10% O2 at total pressures as low as 3 Pa (3×10−2 mbar) and a deposition rate 210 nm/h. Negative oxygen ion‐resputtering has been considerably reduced by introducing a biased copper mask between the substrate and target. The surface morphology and physical properties of the films are greatly improved on applying a positive dc substrate bias with respect to the grounded deposition chamber. We have obtained superconductingYBCOfilms with transport critical current as high as 106 A/cm2 at 77 K and low normal‐state resistivity by this approach. Scanning tunneling microscopy analyses of the films with the best superconducting properties reveal a spiral growth mechanism. However, filmsdeposited by negative dc bias under identical sputtering conditions are insulating. From x‐ray θ‐2θ and rocking curve measurements, we identify the insulating films to be c‐axis oriented Y4Ba3O9 (YBO) films. Furthermore, YBCOfilms could be grown on the YBO layers without any degradation of TC and c‐axis orientation. This novel bias sputtering feature gives us a unique opportunity to produce superconductor/insulator, YBCO/YBO, multilayers from a single YBCO target.